The major objective of the proposed study is to investigate the role of prostaglandins (PGs) and cyclic AMP (cAMP) in cytodifferentiation utilizing chondrogenesis as an in vitro model system. Both cAMP and PGs have been implicated as internal and external regulatory factors, respectively, in chondrogenesis, however, the basis for the proposed regulatory influence of these factors is still unknown. The proposed study will employ high density tissue culture of cells from chick limb buds as a model system for chondrogenesis. In this system, chondrogenesis proceeds through an orderly sequence of morphological and biochemical events, which have been well characterized by previous investigations and which mark specific temporal changes which accompany the expression of the mature phenotype. The study will have three major objectives: 1. To determine the distribution and activation characteristics of cAMP-dependent protein kinase during chondrogenesis and effects of PGs on activation of this enzyme in intact limb cells. 2. To determinme the distribution of endogenous substrate proteins phosphorylated during chondrogenesis and the effects of PGs on protein phosphorylation. 3. To determine the type and relative amounts of PGs synthesized by limb bud cells during chondrogenesis. The study will provide important, new information regarding the possible role of PGs and cAMP in limb chondrogenesis which should broaden our understanding of a variety of skeletal defects which occur during embryogenesis.